Decreased binding of peptides-MHC class I (pMHC) multimeric complexes to CD8 affects their binding avidity for the TCR but does not significantly impact on pMHC/TCR dissociation rate.

The CD8 coreceptor plays a crucial role in both T cell development in the thymus and in the activation of mature T cells in response to Ag-specific stimulation. In this study we used soluble peptides-MHC class I (pMHC) multimeric complexes bearing mutations in the CD8 binding site that impair their binding to the MHC, together with altered peptide ligands, to assess the impact of CD8 on pMHC binding to the TCR. Our data support a model in which CD8 promotes the binding of TCR to pMHC. However, once the pMHC/TCR complex is formed, the TCR dominates the pMHC/TCR dissociation rates. As a consequence of these molecular interactions, under physiologic conditions CD8 plays a key role in complex formation, resulting in the enhancement of CD8 T cell functions whose specificity, however, is determined by the TCR.

Cancer risk in the Swiss HIV Cohort Study: associations with immunodeficiency, smoking, and highly active antiretroviral therapy.

BACKGROUND: Persons infected with human immunodeficiency virus (HIV) have an increased risk for several cancers, but the influences of behavioral risk factors, such as smoking and intravenous drug use, and highly active antiretroviral therapy (HAART) on cancer risk are not clear. METHODS: Patient records were linked between the Swiss HIV Cohort Study and Swiss cantonal cancer registries. Observed and expected numbers of incident cancers were assessed in 7304 persons infected with HIV followed for 28,836 person-years. Relative risks for cancer compared with those for the general population were determined by estimating cancer registry-, sex-, age-, and period-standardized incidence ratios (SIRs). RESULTS: Highly elevated SIRs were confirmed in persons infected with HIV for Kaposi sarcoma (KS) (SIR = 192, 95% confidence interval [CI] = 170 to 217) and non-Hodgkin lymphoma (SIR = 76.4, 95% CI = 66.5 to 87.4). Statistically significantly elevated SIRs were also observed for anal cancer (SIR = 33.4, 95% CI = 10.5 to 78.6); Hodgkin lymphoma (SIR = 17.3, 95% CI = 10.2 to 27.4); cancers of the cervix (SIR = 8.0, 95% CI = 2.9 to 17.4); liver (SIR = 7.0, 95% CI = 2.2 to 16.5); lip, mouth, and pharynx (SIR = 4.1, 95% CI = 2.1 to 7.4); trachea, lung, and bronchus (SIR = 3.2, 95% CI = 1.7 to 5.4); and skin, nonmelanomatous (SIR = 3.2, 95% CI = 2.2 to 4.5). In HAART users, SIRs for KS (SIR = 25.3, 95% CI = 10.8 to 50.1) and non-Hodgkin lymphoma (SIR = 24.2, 95% CI = 15.0 to 37.1) were lower than those for nonusers (KS SIR = 239, 95% CI = 211 to 270; non-Hodgkin lymphoma SIR = 99.3, 95% CI = 85.8 to 114). Among HAART users, however, the SIR (although not absolute numbers) for Hodgkin lymphoma (SIR = 36.2, 95% CI = 16.4 to 68.9) was comparable to that for KS and non-Hodgkin lymphoma. No clear impact of HAART on SIRs emerged for cervical cancer or non-acquired immunodeficiency syndrome-defining cancers. Cancers of the lung, lip, mouth, or pharynx were not observed among nonsmokers. CONCLUSION: In persons infected with HIV, HAART use may prevent most excess risk of KS and non-Hodgkin lymphoma, but not that of Hodgkin lymphoma and other non-acquired immunodeficiency syndrome-defining cancers. No cancers of the lip, mouth, pharynx, or lung were observed in nonsmokers.

Soluble MHC-peptide complexes induce rapid death of CD8+ CTL.

Soluble MHC-peptide (pMHC) complexes, commonly referred to as tetramers, are widely used to enumerate and to isolate Ag-specific CD8(+) CTL. It has been noted that such complexes, as well as microsphere- or cell-associated pMHC molecules compromise the functional integrity of CTL, e.g., by inducing apoptosis of CTL, which limits their usefulness for T cell sorting or cloning. By testing well-defined soluble pMHC complexes containing linkers of different length and valence, we find that complexes comprising short linkers (i.e., short pMHC-pMHC distances), but not those containing long linkers, induce rapid death of CTL. This cell death relies on CTL activation, the coreceptor CD8 and cytoskeleton integrity, but is not dependent on death receptors (i.e., Fas, TNFR1, and TRAILR2) or caspases. Within minutes of CTL exposure to pMHC complexes, reactive oxygen species emerged and mitochondrial membrane depolarized, which is reminiscent of caspase-independent T cell death. The morphological changes induced during this rapid CTL death are characteristic of programmed necrosis and not apoptosis. Thus, soluble pMHC complexes containing long linkers are recommended to prevent T cell death, whereas those containing short linkers can be used to eliminate Ag-specific CTL.

Distinct mechanisms control human naive and antigen-experienced CD8+ T lymphocyte proliferation.

Human Ag-specific CD8(+) T lymphocytes are heterogeneous and include functionally distinct populations. In this study, we report that at least two distinct mechanisms control the expansion of circulating naive, memory, and effector CD8(+) T lymphocytes when exposed to mitogen or Ag stimulation. The first one leads to apoptosis and occurs shortly after in vitro stimulation. Susceptibility to cell death is prominent among primed T cell subsets, and it is inversely correlated with the size of the ex vivo Bcl-2(high) population within these subsets. Importantly, the Bcl-2(high) phenotype is associated to the proportion of responsive CD8(+) T cells, independently of their differentiation stage. The second one depends on the expression of newly synthesized cyclin-dependent kinase inhibitor p16(INK4a) that occurs in a significant fraction of T cells that had been actively cycling, leading to their cell cycle arrest upon stimulation. Strikingly, accumulation of p16(INK4a) protein preferentially occurs in naive as opposed to primed derived T lymphocytes and is not related to apoptosis. Significant levels of p16 are readily detectable in a small number of ex vivo CD8(+) T cells. Our observations reveal that activation-induced p16 expression represents an alternative process to apoptosis, limiting the proliferation potential of activated naive derived T lymphocytes.

Anti-CTLA-4 therapy broadens the melanoma-reactive CD8+ T cell response.

Anti-CTLA-4 treatment improves the survival of patients with advanced-stage melanoma. However, although the anti-CTLA-4 antibody ipilimumab is now an approved treatment for patients with metastatic disease, it remains unknown by which mechanism it boosts tumor-specific T cell activity. In particular, it is unclear whether treatment amplifies previously induced T cell responses or whether it induces new tumor-specific T cell reactivities. Using a combination ultraviolet (UV)-induced peptide exchange and peptide-major histocompatibility complex (pMHC) combinatorial coding, we monitored immune reactivity against a panel of 145 melanoma-associated epitopes in a cohort of patients receiving anti-CTLA-4 treatment. Comparison of pre- and posttreatment T cell reactivities in peripheral blood mononuclear cell samples of 40 melanoma patients demonstrated that anti-CTLA-4 treatment induces a significant increase in the number of detectable melanoma-specific CD8 T cell responses (P = 0.0009). In striking contrast, the magnitude of both virus-specific and melanoma-specific T cell responses that were already detected before start of therapy remained unaltered by treatment (P = 0.74). The observation that anti-CTLA-4 treatment induces a significant number of newly detected T cell responses-but only infrequently boosts preexisting immune responses-provides strong evidence for anti-CTLA-4 therapy-enhanced T cell priming as a component of the clinical mode of action.

The role of interleukin-2 in memory CD8 cell differentiation.

The current literature on the role of interleukin (IL)-2 in memory CD8+ T-cell differentiation indicates a significant contribution of IL-2 during primary and also secondary expansion of CD8+ T cells. IL-2 seems to be responsible for optimal expansion and generation of effector functions following primary antigenic challenge. As the magnitude of T-cell expansion determines the numbers of memory CD8+ T cells surviving after pathogen elimination, these event influence memory cell generation. Moreover, during the contraction phase of an immune respons where most antigen-specific CD8+ T cells disappear by apoptosis, IL-2 signals are able to rescu CD8+ T cells from cell death and provide a durable increase in memory CD8+ T-cell counts. At the memory stage, CD8+ T-cell frequencies can be boosted by administration of exogenous IL-2 Significantly, only CD8+ T cells that have received IL-2 signals during initial priming are able t mediate efficient secondary expansion following renewed antigenic challenge. Thus, IL-2 signals during different phases of an immune response are key in optimizing CD8+ T-cell functions, thereby affecting both primary and secondary responses of these T cells.

Neutrophils contribute to development of a protective immune response during onset of infection with Leishmania donovani.

Neutrophils are key components of the inflammatory response and as such contribute to the killing of microorganisms. In addition, recent evidence suggests their involvement in the development of the immune response. The role of neutrophils during the first weeks post-infection with Leishmania donovani was investigated in this study. When L. donovani-infected mice were selectively depleted of neutrophils with the NIMP-R14 monoclonal antibody, a significant increase in parasite numbers was observed in the spleen and bone marrow and to a lesser extent in the liver. Increased susceptibility was associated with enhanced splenomegally, a delay in the maturation of hepatic granulomas, and a decrease in inducible nitric oxide synthase expression within granulomas. In the spleen, neutrophil depletion was associated with a significant increase in interleukin 4 (IL-4) and IL-10 levels and reduced gamma interferon secretion by CD4(+) and CD8(+) T cells. Increased production of serum IL-4 and IL-10 and higher levels of Leishmania-specific immunoglobulin G1 (IgG1) versus IgG2a revealed the preferential induction of Th2 responses in neutrophil-depleted mice. Altogether, these data suggest a critical role for neutrophils in the early protective response against L. donovani, both as effector cells involved in the killing of the parasites and as significant players influencing the development of a protective Th1 immune response.

Virus-like particles induce robust human T-helper cell responses.

Among synthetic vaccines, virus-like particles (VLPs) are used for their ability to induce strong humoral responses. Very little is reported on VLP-based-vaccine-induced CD4(+) T-cell responses, despite the requirement of helper T cells for antibody isotype switching. Further knowledge on helper T cells is also needed for optimization of CD8(+) T-cell vaccination. Here, we analysed human CD4(+) T-cell responses to vaccination with MelQbG10, which is a Qβ-VLP covalently linked to a long peptide derived from the melanoma self-antigen Melan-A. In all analysed patients, we found strong antibody responses of mainly IgG1 and IgG3 isotypes, and concomitant Th1-biased CD4(+) T-cell responses specific for Qβ. Although less strong, comparable B- and CD4(+) T-cell responses were also found specific for the Melan-A cargo peptide. Further optimization is required to shift the response more towards the cargo peptide. Nevertheless, the data demonstrate the high potential of VLPs for inducing humoral and cellular immune responses by mounting powerful CD4(+) T-cell help.

Polyfunctional HCV-specific T-cell responses are associated with effective control of HCV replication

Rapport de synthèse : L'infection par le virus de l'hépatite C (VHC) a une évolution sévère chez les patients co-infectés par VIH/VHC, de même que chez les patients transplantés hépatiques. Toutefois, les mécanismes impliqués dans cette évolution restent peu clairs. Dans ce travail, nous étudions le profil fonctionnel des cellules T spécifiques dirigées contre le virus de l'hépatite C chez 86 patients mono-infectés par VHC, 48 patients co-infectés par VIH/VHC et 42 patients ayant bénéficié d'une transplantation hépatique. La production d'IFN-Y et d'IL-2 et la capacité de proliférer des cellules T CD4+ et CD8+ sont évaluées après stimulation par des peptides dérivés du VHC. Chez les patients mono-infectés par le VHC, les cellules T spécifiques au VHC sont polyfonctionnelles du point de vue de la sécrétion de cytokines, avec trois profils de sécrétion pour les cellules T CD4+: sécrétion uniquement de IL-2, sécrétion de IL-2 et IFN-y et sécrétion uniquement de IFN-gamma, et de deux profils pour les cellules T CD8+: sécrétion de IL-2 et IFN-y et sécrétion uniquement de IFN-gamma. En revanche, les cellules T spécifiques au VHC chez les individus coinfectés par VIH/VHC et chez les patients transplantés hépatiques ont un profil de sécrétions de cytokines marqué par l'absence de cellules CD4+ sécrétant uniquement l'Il-2 et l'absence de cellules CD8+ sécrétant à la fois IL-2 et IFN-gamma. De plus, la prolifération de cellules T CD4+ et CD8+ spécifiques au VHC est considérablement réduite chez les patients co-infectés par VIH/VHC, comme chez les transplantés hépatiques. La présence de cellules T effectrices uniquement (définies par l'absence de cellules T CD4+ sécrétants uniquement de l'IL-2 et l'absence de cellules T CD8+ sécrétant à la fois IL-2 et IFN-gamma et altération de la capacité proliférative) est associée avec une charge virale VHC significativement plus élevée et une fibrose hépatique plus sévère. Par conséquent, les présents résultats suggèrent la participation de mécanismes immunitaires dans l'évolution accélérée de l'hépatite C chez les patients co-infectés par VIH-1 et chez les patients greffés hépatiques.

Vaccination-induced functional competence of circulating human tumor-specific CD8 T-cells.

T-cells specific for foreign (e.g., viral) antigens can give rise to strong protective immune responses, whereas self/tumor antigen-specific T-cells are thought to be less powerful. However, synthetic T-cell vaccines composed of Melan-A/MART-1 peptide, CpG and IFA can induce high frequencies of tumor-specific CD8 T-cells in PBMC of melanoma patients. Here we analyzed the functionality of these T-cells directly ex vivo, by multiparameter flow cytometry. The production of multiple cytokines (IFNγ, TNFα, IL-2) and upregulation of LAMP-1 (CD107a) by tumor (Melan-A/MART-1) specific T-cells was comparable to virus (EBV-BMLF1) specific CD8 T-cells. Furthermore, phosphorylation of STAT1, STAT5 and ERK1/2, and expression of CD3 zeta chain were similar in tumor- and virus-specific T-cells, demonstrating functional signaling pathways. Interestingly, high frequencies of functionally competent T-cells were induced irrespective of patient's age or gender. Finally, CD8 T-cell function correlated with disease-free survival. However, this result is preliminary since the study was a Phase I clinical trial. We conclude that human tumor-specific CD8 T-cells can reach functional competence in vivo, encouraging further development and Phase III trials assessing the clinical efficacy of robust vaccination strategies.

Inhibitory Receptor Expression Depends More Dominantly on Differentiation and Activation than "Exhaustion" of Human CD8 T Cells.

Under conditions of chronic antigen stimulation, such as persistent viral infection and cancer, CD8 T cells may diminish effector function, which has been termed "exhaustion." Expression of inhibitory Receptors (iRs) is often regarded as a hallmark of "exhaustion." Here we studied the expression of eight different iRs by CD8 T cells of healthy humans, including CTLA-4, PD1, TIM3, LAG3, 2B4, BTLA, CD160, and KLRG1. We show that many iRs are expressed upon activation, and with progressive differentiation to effector cells, even in absence of long-term ("chronic") antigenic stimulation. In particular, we evaluated the direct relationship between iR expression and functionality in CD8 T cells by using anti-CD3 and anti-CD28 stimulation to stimulate all cells and differentiation subsets. We observed a striking up-regulation of certain iRs following the cytokine production wave, in agreement with the notion that iRs function as a negative feedback mechanism. Intriguingly, we found no major impairment of cytokine production in cells positive for a broad array of iRs, as previously shown for PD1 in healthy donors. Rather, the expression of the various iRs strongly correlated with T cell differentiation or activation states, or both. Furthermore, we analyzed CD8 T cells from lymph nodes (LNs) of melanoma patients. Interestingly, we found altered iR expression and lower cytokine production by T cells from metastatic LNs, but also from non-metastatic LNs, likely due to mechanisms which are not related to exhaustion. Together, our data shows that expression of iRs per se does not mark dysfunctional cells, but is rather tightly linked to activation and differentiation. This study highlights the importance of considering the status of activation and differentiation for the study and the clinical monitoring of CD8 T cells.

Tumor-reactive, SSX-2-specific CD8+ T cells are selectively expanded during immune responses to antigen-expressing tumors in melanoma patients.

The SSX-2 gene encodes a tumor-specific antigen expressed in neoplasms of various histological types. By analyzing a tumor-infiltrated lymph node of a melanoma patient bearing an SSX-2-expressing tumor, we have recently identified the first SSX-2-derived CD8(+) T-cell epitope, that corresponds to peptide SSX-2(41-49), and is recognized by specific CTL in an HLA-A2 restricted fashion. Here, we have used fluorescent HLA-A2/SSX-2(41-49) peptide multimeric complexes to analyze the response to SSX-2(41-49) in melanoma patients and healthy donors. Multimer(+) CD8(+) T cells were readily detected in the majority of patients bearing SSX-2-expressing tumors and, at lower proportions, in patients with nonexpressing tumors and healthy donors. Importantly, isolated A2/SSX-2(41-49) multimer(+) CD8(+) T cells exhibited a large functional heterogeneity in terms of antigen recognition and tumor reactivity. SSX-2-specific CTLs isolated from tumor-infiltrated lymph node of antigen-expressing patients as well as from the corresponding peripheral blood mononuclear cells exhibited high functional avidity of antigen recognition and efficiently recognized antigen-expressing tumors. In contrast, SSX-2-specific CTLs isolated from patients with undetectable responses in the tumor-infiltrated lymph node, as well as from healthy donors, recognized the antigen with decreased functional avidity and were not tumor reactive. Together, these data indicate that CD8(+) T-cell responses to SSX-2(41-49) frequently occur in SSX-2-expressing melanoma patients and suggest that SSX-2(41-49)-specific CTLs of high avidity and tumor reactivity are selectively expanded during immune responses to SSX-2-expressing tumors in vivo.

Evidence for a TCR affinity threshold delimiting maximal CD8 T cell function.

Protective adaptive immune responses rely on TCR-mediated recognition of Ag-derived peptides presented by self-MHC molecules. However, self-Ag (tumor)-specific TCRs are often of too low affinity to achieve best functionality. To precisely assess the relationship between TCR-peptide-MHC binding parameters and T cell function, we tested a panel of sequence-optimized HLA-A(*)0201/NY-ESO-1(157-165)-specific TCR variants with affinities lying within physiological boundaries to preserve antigenic specificity and avoid cross-reactivity, as well as two outliers (i.e., a very high- and a low-affinity TCR). Primary human CD8 T cells transduced with these TCRs demonstrated robust correlations between binding measurements of TCR affinity and avidity and the biological response of the T cells, such as TCR cell-surface clustering, intracellular signaling, proliferation, and target cell lysis. Strikingly, above a defined TCR-peptide-MHC affinity threshold (K(D) < approximately 5 muM), T cell function could not be further enhanced, revealing a plateau of maximal T cell function, compatible with the notion that multiple TCRs with slightly different affinities participate equally (codominantly) in immune responses. We propose that rational design of improved self-specific TCRs may not need to be optimized beyond a given affinity threshold to achieve both optimal T cell function and avoidance of the unpredictable risk of cross-reactivity.

Arginase as a marker of disease severity in human leishmaniasis

The leishmaniases are a group of diseases transmitted by the bite of Leishmania infected female phlebotomine sand flies. The diseases occur in different forms: localized, diffuse and muco-cutaneous leishmaniasis, and visceral leishmaniasis (VL). Inside macrophages, the main host cells of the obligate intracellular Leishmania parasites, nitric oxide synthase and arginase can regulate parasite killing or growth. In experimental leishmaniasis, we previously reported that non-healing disease is associated with higher arginase activity at site of pathology, correlating with local suppression of T cell function. To test whether these data translate to human leishmaniasis, the following study was initiated: I first tested the hypothesis that local suppression of T cell responses observed in persistent CL is associated with arginase induced L-arginine depletion. The results showed that arginase activity is increased at site of pathology compared to peripheral blood mononuclear cells (PBMCs) of LCL patients and intact skin of healthy controls. The phenotype of arginase expressing cells was identified in both compartments as CD15+ CD14|0W low-density granulocytes (LDGs). Finally, high arginase activity at site of pathology observed in cutaneous lesions of patients coincides with downregulation of CD3Ç, CD4 and CD8 molecules in CD4+ and CD8+ T cells at site of pathology. We concluded that increased arginase levels in lesions of LCL patients might contribute to CL pathogenesis by impairing T cell effector function at site of pathology. Next, it was tested whether arginase, an enzyme associated with immunosuppression, is higher in patients with VL and contributes to impaired T cell function through depletion of L- arginine. The results showed that higher level of arginase activity in the PBMC coincides with active phase of VL. Cells expressing arginase in PBMCs were also found to be LDGs. Importantly, increased arginase activity and frequency of degranulated neutrophils coincided with lower plasma L-arginine levels. Furthermore, downregulation of CD3Ç, in T cells correlated with low plasma arginine levels. VL/HIV co-infection is a frequently reported leishmaniasis complication in Ethiopia associated with poor prognosis, with up to 40% mortality rate and high relapse rate. Arginase activity was significantly increased in PBMCs and plasma of VL patients co-infected with HIV than in those having VL alone. Similarly, cells expressing arginase in PBMCs were found to be LDGs. In summary, the results presented here show that increased arginase activity is a marker of disease severity in human leishmaniasis with and without HIV; further, these results suggest that arginase mediated L-arginine depletion may inhibit T cell function and contribute to impaired control of infection. - Les leishmanioses sont un groupe de maladies transmises par la piqûre de mouches des sables femelles, appelées phlébotomes, ayant été infectées par Leishmania. Les maladies se manifestent sous différentes formes: la leishmaniose cutanée localisée, la leishmaniose diffuse et mucocutanée et la leishmaniose viscérale (LV). A l'intérieur des macrophages, les principales cellules hôtes des parasites, l'oxyde nitrique synthase et l'arginase, peuvent contrôler, soit la mort du parasite, soit sa croissance. Pour la leishmaniose expérimentale, nous avons déjà rapporté que le développement de lesions qui ne guérissent pas est associé à une activité plus grande d'arginase au site d'infection, en corrélation avec la suppression locale de la fonction des cellules T. Pour vérifier si ces données pouvaient s'appliquer à la leishmaniose humaine, j'ai d'abord vérifié l'hypothèse selon laquelle la suppression locale des réponses des cellules T observée dans la CL persistante, est associée à la la diminution de L- arginine induite par l'arginase. Les résultats ont montré que l'activité arginase est augmentée au site d'infection, par rapport aux cellules mononucléées du sang périphérique (CMSP) de patients LCL et à la peau intacte des contrôles sains. Le phénotype de cellules exprimant l'arginase a été identifié dans les deux compartiments comme des granulocytes CD15+ et CD 14" de basse densité (LDG). Enfin, l'activité arginase élevée au site de la pathologie, observée dans les lésions cutanées de patients, coïncide avec la reduction dde l'expression des molécules CD3Ç, CD4 et CD8 dans les cellules T CD4+ et CD8+ au site de pathologie . Nous avons conclu que l'augmentation des niveaux d'arginase dans les lésions de patients LCL pourrait contribuer à la pathogenèse de la CL, en altérant la fonction effectrice des celllules T au site de la pathologie. Ensuite, nous avons vérifié si l'arginase, une enzyme associée à l'immunosuppression, était plus élevée chez les patients atteints de VL et si elle contribuait à la mauvaise fonction des cellules T par la depletion en L-arginine. Les résultats ont montré qu'un niveau plus élevé de l'activité arginase dans les PBMC correspond à la phase active de la VL. Les cellules exprimant l'arginase dans les CMSP se sont révélées à être de type LDG . Il est important de souligner que l'augmentation de l'activité arginase et la fréquence des neutrophiles dégranulés a coïncidé avec des niveaux inférieurs de L-arginine plasmatique. En outre, la suppression de CD3Ç dans les cellules T correlle avec de faibles niveaux d'arginine plasmatique . Il a été fréquement rapporté que la co-infection VL/VIH est une complication de la leishmaniose en Ethiopie, associée à un mauvais prognostic, un taux de mortalité pouvant atteindre 40% et un pourcentage élevé de rechutes. L'activité de l'arginase a beaucoup plus augmentée dans les CMSP et le plasma de patients atteints de VL et co-infectés par le VIH, que chez ceux seulement attaints de VL. De même, les cellules exprimant l'arginase dans les CMSP sont aussi des LDG. En résumé, les résultats présentés ici montrent que l'augmentation de l'activité de l'arginase est un marqueur de gravité de la la leishmaniose humaine, avec ou sans VIH ; en outre, ces résultats suggèrent que la déplétion de L-arginine par l'arginase pourrait inhiber la fonction des cellules T et contribuer à un contrôle réduit de l'infection. - Les Leishmanioses sont des maladies parasitaires transmises par la piqûre d'une mouche des sables femelle (phlébotome) infectée par Leishmania. La maladie se manifeste sous différentes formes cliniques : la leishmaniose viscérale, une maladie progressive mortelle en l'absence de traitement, la leishmaniose muco-cutanée (MCL), la leishmaniose cutanée diffuse (LCD ) maladie mutilante, qui peut être de longue durée et la leishmaniose cutanée localisée maladie dont on guérit mais laissant une cicatrice inesthétique à vie. La maladie est largement répandue, elle affecte les populations les plus pauvres dans 98 pays et 350 millions de personnes à risque. Globalement on estime à 500.000 les nouveaux cas de la forme viscérale et 1-1.5 million ceux de la leishmaniose cutanée. La leishmaniose est fortement endémique en Ethiopie et se manifeste dans les formes viscérale et cutanée. Le parasite Leishmania infecte et se multiplie dans les cellules du système immunitaire, principalement les macrophages. Les macrophages sont capables de tuer le parasite Leishmania s'ils reçoivent des instructions correctes de la part d'autres cellules du système immunitaire, les lymphocytes. Les macrophages expriment deux enzymes importants, appelés oxide nitrique synthase inductible (iNOS ) et l'arginase, qui sont respectivement associés à la promotion de la mort du parasite et la multiplication. L'enzyme iNOS présent dans les macrophages métabolise l'arginine afin de générer de l'oxyde d'azote (NO) , une molécule effectrice nécessaire pour tuer le parasite . Au contraire, lorsque les macrophages sont activés d'une certaine manière conduisant à l'augmention de la régulation de l'arginase, ils métabolisent l'arginine en polyamines qui favorisent la croissance du parasite. Au cours du développement de la leishmaniose, les lymphocytes ne parviennent pas à transmettre aux macrophages les signaux nécessaires pour tuer le parasite. Les mécanismes cellulaires qui sont la cause de ce défaut, ne sont pas bien compris. En utilisant des modèles animaux, nous avons montré la régulation à la hausse de l'arginase au site de la pathologie, qui s'est traduit par l'altération de la fonction effectrice des lymphoctes. Nous avons initié des études de leishmaniose humaine en Ethiopie afin d'identifier le rôle de l'arginase dans la sévérité de la maladie. Nos résultats montrent, que l'arginase est fortement augmentée dans la lésion des patients CL, et dans le sang des patients VL et ceux co-infectés par VL / VIH. Le niveau d' arginase régulée à la hausse coincide avec l'expression inférieure d'une molécule de signalisation dans les lymphocytes, qui est essentielle à leur bon fonctionnement. En VL actif, l'augmentation d'arginase se traduit par la diminution de l'arginine qui est indispensable à la synthèse de NO et au bon fonctionnement des lymphocytes. Ainsi, l'incapacité des lymphocytes à envoyer des signaux adéquats aux macrophages pourrait être due à la suppression de l'arginine.

Impairment of JCV-specific T-cell response by corticotherapy: Effect on PML-IRIS management?

OBJECTIVE: To investigate the impact of corticosteroids (CS) on the viral-specific T-cell response, in particular the JC virus (JCV)-specific one, in an attempt to determine the optimal timing of CS in the management of progressive multifocal leukoencephalopathy-immune reconstitution inflammatory syndrome (PML-IRIS). METHODS: A blood draw was performed before and 7 days after the administration of IV CS to 24 patients with relapsing multiple sclerosis (MS). The phenotypic pattern of T cells was determined by CCR7 and CD45RA. To assess the impact of CS treatment on proliferative response of JCV-, influenza-, and Epstein-Barr virus (EBV)-specific T cells, a thymidine incorporation proliferation assay was performed. An intracellular cytokine staining assay was performed to determine the effect of CS treatment on the production of cytokine by virus-specific T cells. JCV T-cell assays were performed only in JCV-infected patients with MS as detected by serologies (Stratify) or detection of JCV DNA in the urine by PCR. RESULTS: CS led T cells, CD4+ and CD8+, toward a less differentiated phenotype. There was a significant decrease of EBV-, influenza-, and JCV-specific T-cell proliferative response upon CS treatment. There was a significant decrease in the frequency of interferon (IFN) γ- and tumor necrosis factor (TNF) α-producing JCV-specific CD8+ T cells, but not EBV- or influenza-specific CD4+ or CD8+ T cells. CONCLUSIONS: CS have a profound impact on the virus-specific T-cell response, especially on JCV, suggesting that when CS are considered, they should not be given before the onset of clinical or radiologic signs of IRIS. Studies addressing directly patients with MS with natalizumab-caused PML are warranted. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that methylprednisolone treatment decreases the frequency of JCV-specific CD8+ T cells producing IFN-γ and TNFα, impairing control of JCV, suggesting this should be used to treat but not to prevent PML-IRIS. No clinical outcomes were measured.